Querying IN a passed string

Question

I'm trying to send emails to parents of school children.
On the "create message" form page, the user can select one or
more grades that an email should go to (input checkboxes), and
those are passed as a string ("K ,1 ,2 "). On the action page, I'm
trying to query a table of subscriptions (record is Email, School,
Grade) for the passed grades. There can be more than one grade for
a given email if a parent has two kids, for example.
I'm passing the string just fine. I'm saving the string to a
messages table so we can store which grades in that school got
which email. But when I try to use it in a WHERE statement, it dies
on me.
SELECT DISTINCT Email FROM
Subscriptions WHERE GradeID IN ('#Str_GradeID#') gets me
nothing.
WHERE GradeID IN (#Str_GradeID#) gets
me "invalid column name 'K'" (kindergarten).
WHERE GradeID IN '#Str_GradeID#' gets
me "incorrect syntax near 'K ,1 ,2 '"
Is there even a way to do this? Should I be passing the
grades in a different manner?

Answer 1

Actually, it does have spaces, but I'd be happy if they
weren't there. My field type is char with a value of 2 (I'm new to
building dbs in SQL, so I'm sure there's a better way to do that).
Will try your suggestion now. :)
EDIT: Okay, I've changed them to varchar, and taken out the
spaces that were in there. I put in your code, and it's putting in
the quotes. The IN thingy still isn't working, though.