Being I am not a PADI instructor, I am not completely familiar with their standards. I know recently SSI stopped allowing DSD for those under 10 yrs of age (Used to be 8). The ratios are- 10 & 11 y/o- 2 students to 1 instructor, 12 or older 4 students to 1 instructor. I personally keep the number down to the lower ends, so that I can be within reach of the students at all times. I give very specific instructions that they stay very close to me. I also avoid over weighting students,.. its just not worth it