CHICAGO (AP) — Thousands of striking Chicago public school teachers are rallying at a city park in a show of force as union leaders try to work out details of a tentative agreement with the school district to end a week-long walkout.

The contract negotiations have come down to two main issues: job security and union opposition to a new teacher evaluation process. But teachers also have voiced concerns over classroom conditions, including a lack of books and large class sizes.

And union leaders say they will not end the strike until they see the deal in writing.