Please help them start memorizing the things they must know:
Length
US Customary Metric
12 in = 1 ft 100 cm = 1 m
3 ft = 1 yd 1,000 m = 1 km
Mass
US Customary Metric
16 oz = 1 lb 1,000 g = 1 kg
Capacity
Metric
1,000 ml = 1L
Time
60 seconds = 1 minute
60 minutes = 1 hour