1. A method for grading a user solution to a computing assignment, comprising: receiving a program code submitted by a user, wherein the received program code is the user solution to the computing assignment; activating a plurality of code execution engines, wherein each code execution engine of the plurality of code execution engines is a secured isolated execution environment; executing the program code in the plurality of code execution engines concurrently to produce an answer; determining a grade for the answer based on an expected answer and an approximate grading function, wherein the approximate grading function is determined based on a type of the computing assignment; and returning the grade to the user.