My 6.5 years old & 4 years old son really love playing with this marble run. My 6.5 yr. old son can build some joint runs without any assistant. My younger son enjoys putting the marble in and watch it run round and fall. Don't think he can build a run without help yet. But the game help them to think dynamically and in a logical mind.
The adult also having fun to build the runs.
As mentioned in other people's comment, the downside is the flimsy plastic, which make it not suitable for toddler to build runs.
But it still doesn't stop you having fun. Also good value for money comparing to others brand as it has 75 pieces.