Here's what "A Glossary of Developmental Education Terms," JCRL (1991), 23,
2, pp 1-13 lists on the topic:

"Developmental -- l. a sub-discipline of the field of education concerned
with improving the performance of students. 2. a field of research, teaching,
and practice designed to improve academic performance. 3. a process utilizing
principles of developmental theory to facilitate learning." p.4

"Remedial -- instruction designed to remove a student's deficiencies in basic
entry or exit level skills at a prescribed level of proficiency in order to
make him/her competitive with peers." p.9

Although the 33 "experts" who developed the glossary semantically identify
the two terms in ways that would satisfy users who want to employ the terms
both tactically and with professional/political "correctness," truth is the
terms are virtually convertible except that one suggests need for
"improvement" while the other suggests need for "remedy."  My regional
experience is that east of the Mississippi "developmental" is in fashion;
west of the Mississippi, "remedial" has the usage edge.  As long as ACT, ETS,
College Board, League for Innovation, ERIC, Clifford Adelman (U.S. Department
of Education), and, intermittently, John Roueche (U. of Texas)  continue to
use "remedial" without apology, perhaps so might we.

Irreverently yours,

Gene Kerstiens
Andragogy Associates