If college isn't included in a divorce decree, can a parent go back to court to ask the other parent to pay half of college

No.  There is no obligation in Virginia to pay for college expenses for children. This answer is given in accordance with the laws of Virginia and may not be applicable in any other state.  It should not be construed as legal advice, as that would require a more thorough analysis of all of the facts involved in a specific case.  If you need further information or assistance, please feel free to contact my office for a consultation. Case results depend upon a variety of factors unique to each case. Case results do not guarantee or predict a similar result in any future case.