Personally I wouldn't use a Spad for training new pilots. Using the reasoning that "it survives crashes" just justifies the chance that it's going to crash. I've been training people for 11 years and I've never had a student crash is plane while we were on the buddy box, so that's not an issue IMHO. While Spads do fly well and are an inexpensive alternative it's been my experience that they still don't fly as well as a traditional trainer built from balsa. Get them a standard trainer and don't worry about crashing it, that's what you're there for!!
To save them!!!
I realize that the student may have gotten into a situation that was difficult to recover from, but as the instructor you shouldn't have let him get to that point until you were absolutely certain that he was capable of flying at lower altitudes. I do understand that some students want to do what they want and may fly low, but as the instructor with the buddy box you are in control of everything that happens with that plane. If the student gets lower than you feel they are capable of flying at then you simply take control of the plane and gain altitude before giving it back them. Simply explain that you don't think they're ready to fly that low yet. Remember, you are the instructor. I had a student like that once. He thought that he was too good to simply fly a figure 8 pattern. He wanted to do aerobatics, loops, rolls, and such. I would take it from him, level it out, and than tell him he needed to fly the figure 8 pattern until I felt he was able to properly control the plane. I would give it back and he would fly maybe one figure 8 and then start stunting again. This went on 3 or 4 times before I finally took control of his plane, landed it, taxied into the pits, unhooked my buddy box, and walked off. I told him that if he wanted me to instruct him to fly he needed to follow my instructions, and that if he wasn't going to do that then he could go find another instructor or do it on his own. But I was done because I was wasting my time until he decided to follow my instructions. He apologized and we went back up where he did follow my instructions. 2 weeks later he soloed and is now flying on his own.
Hope this helps
Ken