Let and be an Eisenstein series and a cusp form, respectively, of the same weight and of the same level , both eigenfunctions of the Hecke operators, and both normalized so that . The main result we prove is that when and are congruent mod a prime (which we take to be a prime of lying over a rational prime ),
the algebraic parts of the special values and satisfy congruences mod the same prime. More explicitly, we prove that, under certain conditions,

where the sign of is depending on , and
is the corresponding canonical period for . Also, is a primitive Dirichlet character of conductor ,
is a Gauss sum, and is an integer with such that
. Finally, is a -adic unit which is independent of and . This is a generalization of earlier results of Stevens and Vatsal for weight . The main point is the
construction of a modular symbol associated to an Eisenstein series.