Milk for 4 year old

What brand of packet milk do kids almost 4yrs old take? My kid has been on toddler formula and prefers the bottle. His school is weaning all the kids off milk bottle and requested parents to let kids drink milk from a packet. I have a feeling he just prefers the bottle for milk rather than in a packet. He drinks ribena from a packet and can drink water from a cup but just refuses to drink milk from a straw, packet or cup. Any suggestions welcome!