Yes, a big difference!
Hail is usually formed in the warmer months during thunderstorms.
Water droplets get pushed to great heights in the atmosphere by the thunderstorm's updraft.
These small water droplets attach to small particles of dust.
The water droplets freeze to create a hail stone.
The stone starts to fall and is then recaptured by the updraft.
The process continues to repeat itself until the stone gets too heavy and falls out.
The more trips a stone makes through a thunderstorm will determine its eventual size.
Sleet, on the other hand, is formed during colder months.
Sleet forms as water droplets that fall from the cloud as water, but they freeze BEFORE they hit the Earth's surface.