AUGUSTA (AP) — Maine’s top education official says public school districts can now take up to two extra years to implement new proficiency-based graduation requirements if they need the time.

Education Commissioner Jim Rier spelled out six ways to apply for extensions in a letter Wednesday to superintendents.

Under the new system, created by a 2012 Maine law, public schools would ultimately graduate students based on their mastery of eight subject areas — including English, math and science — not just their completion of core credits. The new standards were scheduled to apply starting with this fall’s freshman class.

The Portland Press Herald (http://bit.ly/1oN4LbO ) reported that Rier wrote the two-year extension option was implemented after he heard from education stakeholders concerned about “the complexity of developing quality proficiency-based learning systems.”