This year for the first time, the Illinois legislature is requiring the PSAE as a prerequisite to graduation from a public school. If you are a Senior and did not take the PSAE last Spring, you MUST take it this April. Previously a student could substitute the ACT score from a national administration of the test to meet the PSAE "requirement." That is no longer acceptable.
You must have a PSAE score on your permanent high school transcript in order to qualify for graduation, but don't worry too much about the level of the score. If you're already accepted at the college of your choice, there is little chance that you will be turned away now.
To read instructions from the State Board of Education to public high schools regarding the new legislation, click on the link
and go to the publication titled 2009-10 Guidance - PSAE & the Receipt of a Regular High School Diploma (posted 9/30/09).