Even though the word group because he was not educated has a subject and verb, it does not contain a complete thought and should not be punctuated as if it were a sentence. Note that the word group he was not educated could be punctuated as a sentence. When because is added, the thought is no longer complete. We expect more before the period.

Correction: Because he was not educated, he was ignored.

Check the following resources for useful practice material: 1) Guide to Grammar and Writing, 2) Colleen Hildebrand's UCI Correction Symbols with hyperlinks.

For more about fragments, check the LARC Electronic Writing Center Grammar Checklist.