Does it have to be SD? There are other, less stressful, parts of the country with better quality of life and good schools, including La Romana (Abraham Lincoln School) and Punta Cana (PC International School, Cap Cana Heritage, Bavaro Bilingual).
With the new highway the capital is only one hour from LR and less than 2 hours from PC.
I had considered Punta Cana (CCHS), but it is more realistic to consider Sto Dgo in terms of opportunities for my wife and extracurriculars for our son. I haven't considered Santiago as I'm not familiar with it.