Why would you waste your time drinking 190 calorie beverages when trying to gain weight? He should be drinking 2,000 calorie shakes to put on mass.
It's pretty simple.
Teach him how to eat breakfast, lunch and dinner like a man. Each meal he should be shoveling away at least 1,000 calories.
Breakfast Example: Omelette and Reeses Oatmeal =1,050 kcal
6 whole eggs, 1-2 servings cheese - 550 cals
1/2 cup dry oats, 2tbsp peanut butter, 1 scoop chocolate whey - 500 cals
Lunch Example: Grilled Chicken Thighs and Baked Sweet Potato =1,000 kcal
16 oz grilled boneless skinless chicken thighs w/ barbecue sauce - 600 cals
3 medium sweet potatoes (microwave 4 min/side covered in damp paper towel) - 400 cals
Dinner Example: Muscle Chili - 1,300 cals
16 oz lean ground beef - 800 cals
1/2 can beans - 250 cals
2 servings cheese - 250 cals
use cumin, paprika, salt, pepper. Can steam some brown rice and pour over if you want more calories/carbs. This is great hot or cold any time of year.
Post-Workout/Anytime Shake: 1,300 - 1,800 kcal
2 cups whole milk or almond milk 200-400 cals
4 tbsp peanut butter - 400 cals
4 tbsp olive or coconut oil - 400 cals
1-2 scoops chocolate whey - 140-280 cals
1 banana - 150 cals
optional - small handful spinach, mixed frozen berries, misc. fruit.
This is roughly what I eat every day, 4,650-5,150 calories. That's how you eat like a man. He probably eats about 2,500 calories at most if he weighs 130.
If he can't handle this much food at once, tone it down to 12 oz of meat at lunch and dinner, 2 sweet potatoes, maybe 4 instead of 6 eggs but keep the calories up above 4,000! He will gain weight in no time and realize how hard it is to eat like he needs to be.
Slim Fast? Gimme a break.