filtering a form

[Betsy]

I have a form that filters students based on the school
that they attend. I need to accommodate a second school
as some students attend a second school half days. I do
not want to list the student twice in the table because I
can't track all their activities that way. I have added
a check box to the student table if they attend the
second school they can check it.
Student table looks like this:
StudentID AutoNumber
StudentFirstName Text
StudentLastName Text
SchoolID linked to School Table
SCT Yes/No

I built a query to filter the form based on the School.
When you select a school all the students in that school
are available in the Student Combo Box. The query uses
the following expression under SchoolID
[Forms]![frmEventDup]![frmLinkStudentDup]![SchoolID]

How do I incorporate the check box to indicate that they
attend this other school???