By TMZ Sports

Former world champion Zab Judah beat people up for a living ... but now he's got another job, assisting elderly patients with dementia, and helping teach a nursing class.

Judah -- a four time world champ -- is working at an adult day care facility during the day, and helping teach a nurses assistant class by night ... all the while still training as a pro fighter.

Teberah Alexander -- the director at Excelling Nursing Academy who also runs the day care facility -- tells TMZ Sports that Judah recently graduated the nurses assistant class (he's now CPR certified, and First-Aid trained) ... and now actually helps teach a class of students studying to get certified.

Alexander says Zab primarily works with people with dementia and Alzheimer's ... and has developed a bond with the elderly patients.

She says Zab does everything from catheters to taking vitals.

it's no secret that Zab has had his fair share of trouble in the past ... but we're told that Judah has changed his life, and has been a favorite of patients, staff and students at the nursing facility.

Judah (43-9, 30 KOs), 40 years old, has been out of the ring since January, when he made his comeback to score a two round KO win. It was Judah's first bout since losing to Paulie Malignaggi in December 2013. There is no word if Judah intends to resume his boxing career.

IN OTHER NEWS: Eight members from the "Pound-4-Pound" gym, Las Vegas' # 1 amateur boxing program, will compete in the 2017 USA Boxing Elite Youth National Championships & Junior Open. The five-day tournament will take place in Salt Lake City, UT, at the Calvin L. Rampton Salt Palace Convention Center, more commonly known as the Salt Palace, starting December 5th through December 9th.

Only the best boxers from around the United States will compete to see who is the best amateur boxer in the nation. All 15 and 16 year-olds who win this tournament will make the USA Boxing Team. All others will be ranked #1 in their respective weight classes.