You need to weigh in more than once and keep as many things constant as possible (ie. time of day, food before weighing, clothing worn, etc.). Get him to weigh in everyday (or everyday he does cardio) and see how/if it varies.
I would give it a bit more time. You've got cardio 3-4 times a week and since he's a week and a half in, thats only like 4-6 sessions on the treadmill. If he's eating less than maintenance, weightloss should occur. Unless your maintenance is high.
Threaded Mode