Use quotation marks to turn words into phrases. For example, searching for either "working mothers" or "common core" will only give you search results where the two words are used together as a phrase. When you search these words without the quotation marks, your results will show one word or the other, and sometimes both together, so using quotation marks guarantees that both of your search terms will be in the articles in your results list.
In most, but not all, databases, using an asterisk at the end of a word will search for all variations of that word. For example, searching for "educational strategy*" will give you search results containing either "educational strategies" or "educational strategy," as well as other variations of the phrase.