Neither student loan companies nor the government should get rich off student loans. They are an investment in future labor. Government will benefit later from high-skilled workers making higher wages and paying higher taxes. Corporations will profit later by having richer citizens able to spend more in the economy. Short-term profits should thus be minimized in favor of making college and graduate education more affordable and easier to access.
To that end, both public and private interest rates should be capped at 3% and no student loan company should be permitted to use any other formula but simple interest. Interest may not be prepaid before reaching the principal. This will lower monthly payments by making it easier to pay off balances, further reducing the interest charges.