When you log into SchoolMint, you can see the Waitlist number, by school. As spots open up, schools then go to the top of the Waitlist and offer seats. If you get a spot, the school will call you and give you the offer to attend that school. You must accept or decline the offer on SchoolMint. The Waitlist stays open through the third week of the next school year.
A common question is what happens when I get accepted to my second choice school? Look at this scenario for three fictional schools. The lottery ran and the child was offered a spot at The Daisy School. The child will still stay on the Waitlist for any school above the ranking; so the child stays on the The Rose School Waitlist through the first three weeks of the new school year. The application is cancelled to The Sunflower School (because the parent accepted The Daisy School).