Around 1,500 parents are yet to apply for a primary school place for their child, despite the deadline approaching, said the Lincolnshire County Council.
The deadline to hand in school applications is next week on January 14, but the local authority is yet to receive the important forms.
If a parent misses the deadline, there is no guarantee they will get their child into the school they want.
Children born between September 1 2006 and August 31 2007 need a form so they can attend a school of choice this September.
Attending a school’s nursery or already having a sibling at the school also does not guarantee a place there.
The County Council are urging parents to pick up an application pack from any school and hand it in quickly to get their school of choice.
Parents can also get a form by calling the council on 01522 782030 or apply online.
Director of Children’s Services Peter Duxbury said: “We are concerned that we still haven’t received so many outstanding applications.
“Parents who apply late can be at a disadvantage and may not be offered the school they want.
“So don’t delay, apply today — time is running out.”
Schools can also help parents fill out the form and offer advice, and there is no need for an appointment to discuss school placements.