Here is one definition of evaluation.
Evaluation is a systematic process for an organization to obtain information on its activities, its impacts, and the effectiveness of its work, so that it can improve its activities and describe its accomplishments.
Mattessich PW. The Manager's Guide to Program Evaluation. St Paul, MN: Wilder Research Center. 2003.
A key phrase is "systematic process," which implies it takes some thinking and planning and is not a one-time activity. All too often people wait until a grant opportunity or until a program has ended to try to determine its effectiveness. Unfortunately, this means there is no baseline information for comparing any subsequent data, and thus no way to document progress. Creating an evaluation plan at the beginning of the program and implementing it will solve this problem. Think about 1) the purpose of the evaluation, 2) who will use the evaluation results and 3) how the results will be used. Evaluation plans should reflect various stages of your program with accompanying timelines. The focus of evaluation early in your program (after a few months) will probably look more at process measures to determine if changes need to be made in staffing, program operations, marketing, etc. It will be too early to measure oral health outcomes -- these generally take at least a year or more to measure.