Here are some general guidelines that will help you determine if your child is ready to move to a booster seat.
Car seat safety Caring for kids
Should Your Child Still Be Using a Booster Seat? - Consumer Reports
Is Your Child Ready for a Booster Seat? - Buckle Up for Life
Booster Seat Requirements, Booster Seat Age
Does Your Child Pass The 5 Step Test?
High-Back vs Backless Booster Seats
High-Back vs Backless Booster Seats
Transitioning to a seat belt : – Securing North Carolina for Life
When is my child ready for a high back booster?