Sean “Diddy” Combs is using his time in jail to teach his fellow inmates business skills … and the men who picked his brain are singing his praises to the judge who is set to hand down his sentence next week.

Diddy’s legal team is giving Judge Arun Subramanian more legal homework in the form of additional support letters from dozens of men who are locked up with Diddy at MDC Brooklyn.

In the letters, included in a legal filing obtained by TMZ, the inmates say they took the Bad Boy Records founder’s “Free Game With Diddy” course behind bars and learned a lot.

Here’s a sampling of what the jailbirds are saying:

Arturo Santiago writes, “Because of this class I have a purpose, something to look forward to every day.”

Douglas Welch says, “He has showed us that it is the little adjustments to our everyday lives that add up to a big change.”

Wellington Eustate explains, “Mr. Combs teaches us about how chasing the easy money is the wrong way to achieve greatness.”

Didier Rios Galinda recalls, “Everybody was motivated for the lesson … in my case particularly it has had very much impact.”

Quinton Davis notes, “The Free Game class with Mr. Combs has affected me in a good way and has impacted me because I’ve learned many things like how to create a successful plan. And that plan has to be realistic.”

Charles Scruggs says, “I was really appreciative to receive some knowledge of sort to take back to the real world an[d] not have to think about doing something illegal. He taught me to come up with a plan.”

Corey Batchelor writes, “The class has given me something to look forward to doing while being incarcerated and now I am currently beginning to study on a new business venture and coming up with a plan so when I am released I can more forward with it and live a positive life.”

Raymond Castillo says Diddy “saved me” and says he’s witnessed Diddy “do magical things” behind bars with limited resources. He says, “In a place of segregation [I] have seen Mr. Combs bring unity to all races and ethnics groups no matter the background as a unified front.”