Perhaps you should try some spelling variations:
"math skills series." » "math skills surveys.", "math skills service.", "math skills studies.", "mat skills series.", "path skills series."
"motor skills series." » "motor skills surveys.", "motor skills service.", "motor skills studies.", "labor skills series."
"labor soil surveys." » "labor social surveys.", "labor school surveys.", "labor skills surveys.", "labor skill surveys.", "labor sri 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 ("motor skills series."))) or ("labor soil surveys."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (((("math skills series.") OR ("motor skills series."))) OR ("labor soil surveys."))*.
• Removing quotes may allow a broader search: (((( math skills series. ) or ( motor skills series. ))) or ( labor soil surveys. ))*.