What test to use?

Which statistical test would you use to analyze data from a quasi-experimental comparison Group Pre-test/Post-test?

Subjects are nonrandomly assigned to the treatment and non-treatment groups.

I tried searching online, and it appears that I have to use an ANCOVA? Since the statistical analysis is obviously beyond me, I am looking for suggestions on which tests / statistical topics I should study so that I can analyze the data.

Thanks for any help.
Hi Dason, thank you for your reply. The subjects were students, and the treatment was a tutoring program. Students were selected to receive treatment based on their classroom performance and amount of support they had at home. The students with the highest need were referred into the program. Unfortunately, there was no single test or cut-off point used to determine if the students should receive the program.

EDIT: I believe the design I used is called the nonequivalent groups design (http://www.socialresearchmethods.net/kb/quasnegd.php)

Since both pre and post tests were measured on the same metric (same standardized assessment tool), does that mean I can simply compare the differences of post minus pre test scores? And if so, which test would I use?
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