Perhaps you should try some spelling variations:
"improving human performance series." » "improving human performance studies.", "improving human performance size.", "improving loan performance series.", "improving thermal performance series.", "improving chain performance series."
"improving pupil performance series." » "improving pupil performance studies.", "improving pupil performance size.", "improving social performance series.", "improving model performance series.", "improving judicial performance series.", "improving public performance series.", "improving civil performance series.", "improving audit performance series."

Try widening your search to All Fields.

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("improving human performance series.") or ("improving pupil performance series."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving human performance series.") OR ("improving pupil performance series.")).
• Removing quotes may allow a broader search: (( improving human performance series. ) or ( improving pupil performance series. )).
• Adding a wildcard symbol may retrieve word variants: (("improving human performance series.") or ("improving pupil performance series."))*.