Perhaps you should try some spelling variations:
"improving teacher performance series." » "improving sector performance series.", "improving teacher performance studies.", "improving teacher performance size.", "improving teaching performance series.", "improving gender performance series.", "improving trade performance series."
"improving poor performance metrics." » "improving poor performance measures.", "improving sector performance metrics.", "improving power performance metrics.", "improving food performance metrics.", "improving peer performance metrics."

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

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