Perhaps you should try some spelling variations:
"math skills studies." » "math skills student.", "mat skills studies.", "path skills studies."
"math skills series." » "math skills surveys.", "math skills service.", "math skills survey.", "mat skills series.", "path skills series."
"motor soil surveys." » "motor social surveys.", "motor school surveys.", "motor skills surveys.", "monitor soil surveys.", "motor skill surveys.", "poor soil surveys."

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (((("math skills series.") OR ("math skills studies."))) or ("motor soil surveys."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (((("math skills series.") OR ("math skills studies."))) OR ("motor soil surveys.")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"math skills series.\") OR (\"math skills studies.\"))) or (\"motor soil surveys.\"))".
• Removing quotes may allow a broader search: (((( math skills series. ) OR ( math skills studies. ))) or ( motor soil surveys. )).
• Adding a wildcard symbol may retrieve word variants: (((("math skills series.") OR ("math skills studies."))) or ("motor soil surveys."))*.