Students tend to forget a lot that they learned in the past year over the summer. This is unfortunate and leads to review of past material in the new school. Progress is slowed which can put the class behind. Children need summer learning to keep their minds sharp and active. The learning motivation needs to remain strong.
I don't know about you, but I don't know any kid that stops learning over the summer, even when he or she is not in class. Learning is not confined to the classroom, and students that are able to have free time are also learning. So yes, summer learning can make our children smarter, but I don't think that should necessarily be in the classroom.
Anything to help our children's minds progress is a blessing. For a child to be involved in structured learning during the summer months is far better than for them to be idle in everything but video games. Their brains need a break from normal school curriculum however, it doesn't hurt to a mild form of education into the summer package
Of course summer learning can make kids smarter. The more time a child spends in the classroom the better off they will be. The time of year is irrelevant. A child that works hard and learns during the summer will obviously be ahead of one that chooses not to learn during the summer.