Sleep is an active process influenced by circadian rhythms, aka your internal clock. During sleep, your body puts your immune system in high gear, clears your brain, improves cognitive function, and maintains emotional stability.
Sleep is the body's designated time for growth, maintance, and recovery. The closer child is to getting the appropriate quantity and quality of sleep, the better you are setting child up for proper growth and development.
During sleep, the body increases the levels of human growth hormone (HGH) that is circulating in the body. The body goes through other metabolic and homeostatic mechanisms that aid and prepare the body for growth. Not get enough sleep does not provide the body time to grow.
When you are sleeping, your brain rebuilds its neurons or works to shift the structure to adapt to the needs. The maintance of neurons promotes faster response time, better recall/memory, and helps nail down muscle memory. Biologically, learning is the neurological change, and neurological changes happen at a much faster rate during sleep. Therefore, making sure your child is getting adequate sleep will help them in the classroom.