In the Houston area have him look up WETS (
http://wetscourses.com) . They have the Irrigator Licensing Class in the Houston Area fairly often likely monthly to every other month.
Its a big investment by the time you pay for classes ($500), exam ($120) and licensing application ($111) for a student wanting to make money on the side. Also it is not a quick process to get licensed and he is very behind if he wants to get licensed this summer.
I've been an LI since 2008 but was working in Ag irrigation for 4 years prior to that. I work more on the consulting and education side but manage to squeeze in a good handful of repairs after regular hours during the summer.
You dont have to have a lot of special equipment to get started out as but you do need to have a basic inventory to do timely repairs. I have a big plastic tub of pvc fittings and another of sprinklers and valves with about 5ft of 1/2". 3/4" and 1" pipe in my truck that gets me through most repairs, i dont have everything so there is still the occasional run to the supplier.