I look at this as a happy problem. Students will go on ahead, but with coding you have to watch out for people to get stuck, the famous spots are "random hurdles" and "Caterpillar" although there are others. If you can try to have students working with others it will help them avoid being "stuck".
If you feel that you want them to stay close together I would consider having them code in the sandbox, i.e. create original and unique examples of code that they can really call their own. Our students love the sandbox.