Assuming you want to begin graduate/professional
school the September immediately following
graduation, the GRE, GMAT and Millers
Analogies can typically be taken
during the senior year. The more competitive
the program to which you have applied,
the earlier you should take the appropriate
test. Spring of the junior year is
not too early to test for particularly
competitive programs.
LSAT and MCAT are typically
taken during the second half of the
junior year to allow sufficient time
for the highly rigorous admissions
process.