I use the school glue too. I buy a gallon of it and a I buy smaller bottle of it that I can refill as the smaller size is easier for me to hold on to. I squeeze a thin line on it and use any kind of stiff plastic I have laying around to use as a spreader and spread the glue as best I can. I don't want the glue to dry in lines (maybe 10" apart) and be lumpy. I worry about the spray glues. I don't know of any that says it'll wash out, and I don't want the chemicals to become a problem years downline. I don't know of any studies that exam how those spray glues affect the cotton over time. I glue both the front and the back before I quilt it.