<Page>

                                                                     EXHIBIT 5.1

                                October 29, 2001


USA Education, Inc.
11600 Sallie Mae Drive
Reston, Virginia 20193

Ladies and Gentlemen:

         I am Executive Vice President and General Counsel of USA Education,
Inc. (the "Corporation") and, as such, I have acted as counsel for the
Corporation in the preparation of a Registration Statement on Form S-3 (File No.
333-63164) (the "Registration Statement") filed with the Securities and Exchange
Commission under the Securities Act of 1933, as amended (the "Securities Act")
in connection with the proposed offer and sale of the following securities from
time to time (the "Securities") of the Corporation having an aggregate initial
offering price of up to $3,000,000,000: (i) debt securities (the "Debt
Securities"), (ii) preferred stock, par value .20 per share (the "Preferred
Stock"), (iii) common stock, par value .20 per share (the "Common Stock"), of
the Corporation issuable upon conversion of Debt Securities or Preferred Stock,
or upon exercise of warrants or in connection with the settlement of privately
negotiated equity forward purchase contracts, and (iv) warrants to purchase Debt
Securities, Preferred Stock, or Common Stock; warrants or other rights relating
to foreign currency exchange rates; or warrants for the purchase or sale of debt
securities of, or guaranteed by, the United States government or its agencies,
units of a stock index or stock basket or a commodity or a unit of a commodity
index (collectively, the "Warrants"). The Securities may be offered separately
or as part of units with other Securities, in separate series, in amounts, at
prices, and on terms to be set forth in the prospectus and one or more
supplements to the prospectus (collectively, the "Prospectus") constituting a
part of the Registration Statement, and in the Registration Statement.

         The Debt Securities are to be issued under one or more indentures in
the form to be filed with the Securities and Exchange Commission, with
appropriate insertions (the "Indenture"), to be entered into by the Corporation
and a trustee or trustees to be named by the Corporation. Each series of
Preferred Stock is to be issued under the Certificate of Incorporation, as
amended, (the "Certificate of Incorporation") of the Corporation and a
certificate of designations (a "Certificate of Designations") to be approved by
the board of directors of the Corporation or a committee thereof and filed with
the Secretary of State of the State of Delaware (the "Delaware Secretary of
State") in accordance with section 151 of the General Corporation Law of the
State of Delaware. The Common Stock is to be issued under the Certificate of
Incorporation. The Warrants are to be issued under a warrant agreement in the
form to be filed with the Securities and Exchange Commission, with appropriate
insertions (the "Warrant Agreement"), to be entered into by the Corporation and
a warrant agent to be named by the Corporation.


<Page>


USA Education, Inc.
October 29, 2001
Page 2

         Certain terms of the Securities to be issued by the Corporation from
time to time will be approved by the Board of Directors of the Corporation or a
committee thereof or certain authorized officers of the Corporation as part of
the corporate action taken and to be taken (the "Corporate Proceedings") in
connection with issuance of the Securities. I have examined or am otherwise
familiar with the Certificate of Incorporation, the By-Laws of the Corporation,
as amended, the Registration Statement, such of the Corporate Proceedings as
have occurred as of the date hereof, and such other documents, records, and
instruments as I have deemed necessary or appropriate of the purposes of this
opinion.

         Based on the foregoing, I am of the opinion that (i) upon the execution
and delivery by the Corporation of the Indenture and the execution and delivery
of the Warrant Agreement, the completion of all required Corporate Proceedings,
and the execution, issuance, and delivery, and the authentication by a duly
appointed trustee, of the Debt Securities and the Warrants, respectively,
pursuant to such agreements, such Indenture, or Warrant Agreement, as the case
may be, any Debt Securities issuable thereunder will be legal, valid, and
binding obligations of the Corporation, and any Preferred Stock (assuming
completion of the actions referred to in clause (ii) below) or Common Stock
(assuming completion of the actions referred to in clause (iii) below) issuable
thereunder will be duly and validly authorized and issued, fully paid, and
nonassessable; (ii) upon the authorization, execution, acknowledgment, delivery,
and filing with, and recording by, the Delaware Secretary of State of the
applicable Certificate of Designations, the completion of all required Corporate
Proceedings and the execution, issuance and delivery of the Preferred Stock
pursuant to such Certificate of Designations, the Preferred Stock will be duly
and validly authorized and issued, fully paid, and nonassessable; and (iii) upon
the authorization of issuance of the Common Stock, the completion of all
required Corporate Proceedings, and the execution, issuance, and delivery of the
Common Stock, the Common Stock will be duly and validly authorized and issued,
fully paid, and nonassessable; except in each case as enforcement of provisions
of such instruments and agreements may be limited by bankruptcy or other laws of
general application affecting the enforcement of creditors' rights and by
general equity principles. The foregoing opinions assume that (a) the
consideration designated in the applicable Corporate Proceedings for any
Preferred Stock or Common Stock shall have been received by the Corporation in
accordance with applicable law; (b) the Indenture and Warrant Agreement shall
have been duly authorized, executed, and delivered by all parties thereto other
than the Corporation; (c) the Registration Statement shall have become effective
under the Securities Act and will continue to be effective; (d) the Indenture
shall have become duly qualified under the Trust Indenture Act of 1939, as
amended; and (e) that, at the time of the authentication and delivery of the
Securities, the Corporate Proceedings related thereto will not have been
modified or rescinded, there will not have occurred any change in the law
affecting the authorization, execution, delivery, validity or enforceability of
such Securities, none of the particular terms of such Securities will violate
any applicable law and neither the issuance and sale thereof nor the compliance
by the Corporation with the terms thereof


<Page>


USA Education, Inc.
October 29, 2001
Page 3


will result in a violation of any agreement or instrument then binding upon the
Corporation or any order of any court or governmental body having jurisdiction
over the Corporation.

         I have also assumed (a) the accuracy and truthfulness of all public
records of the Corporation and of all certifications, documents and other
proceedings examined by me that have been produced by officials of the
Corporation acting within the scope of their official capacities, without
verifying the accuracy or truthfulness of such representations, and (b) the
genuineness of such signatures appearing upon such public records,
certifications, documents and proceedings. I express no opinion as to the laws
of any jurisdiction other than the laws of the District of Columbia, the General
Corporation Law of the State of Delaware, and the federal laws of the United
States of America. I express no opinion as to whether, or the extent to which,
the laws of any particular jurisdiction apply to the subject matter hereof,
including, without limitation, the enforceability of the governing law provision
contained in the Indenture or the Warrant Agreement. Because the governing law
provision of the Indenture or the Warrant Agreement may relate to the law of a
jurisdiction as to which I express no opinion, the opinion set forth in clause
(a) of the preceding paragraph are given as if the law of the District of
Columbia governs the Agreements.

         I hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to being named in the Prospectus included therein
under the caption "Legal Matters" with respect to the matters stated therein
without implying or admitting that I am an "expert" within the meaning of the
Securities Act, or other rules and regulations of the Securities and Exchange
Commission issued thereunder with respect to any part of the Registration
Statement, including this exhibit.

                                       Very truly yours,


                                       /s/ MARIANNE M. KELER
                                       Marianne M. Keler