Or just stick them on national service for a few years
Easier to legalise drugs, remove the reason for the majority of knife crime/imprisonment, tax and legislate the sale and use the revenue for community, health and social projects in deprived areas.
It has been over 50 years fighting a losing battle and drug usage around the world is higher than ever. Probably no adult under the age of 70 in the UK who couldn't get a gram of coke within a few hours. Time to accept defeat.