Since you can hang back and deal with incoming enemies, you can try that. Outside the school, you will face some Locust with One Shot heavy sniper weapons. For the most part, the Hammerburst / Lancer combination will be more serviceable. There is a Retro Lancer in the gated section if you feel the need to have a wildly more inaccurate weapon with half the ammunition. The exit the Wretch blocked in the cut-scene gives you a perfect cul-de-sac to hole up and commit mass murder.

It may be handy to stay there with a Lancer and wait for them to come to you. Head into the basement and trigger the Wretch attack by going towards the partly open gate. You can keep moving while everything is dark - there are no enemies until you get to the basement.