Summer School Riddle

I'm stuck in summer school because of mumble mumble. And to make matters worse, we have a test at the end of the week.

But our teacher said, if we aced the coming test, we'd be free to go and would not need to come back until the start of the school year in the fall.

She said that all we needed to remember was a simple saying. Then she wrote this on the board:

An exception to the rule
That many find so minuscule

The perfect son of jack implore
Start at the beginning, and three more

Of a president and a state,
Only one did mutate

I really want to get my summer back, and I know how good some of you are at riddles.

So, what saying does she want us to remember?

She took pity on us today and gave us a hint:

This is a problematic rule of thumb,
That so many find ho-hum

HINT #2:

Wrong is the post,

Everything above will be kept in character. Comments to answers will not be in character.

Could it be...

"i before e, except after c"?

An exception to the rule
That many find so minuscule

It talks about an exception to a short spelling rule

The perfect son of jack implore
Start at the beginning, and three more

Intended
Jackson 5 had a song "ABC" that used this line in the lyrics

Original
"i" looks like a short version of "j"? and "cei--" are the first three letters in a word following this rule

Of a president and a state,
Only one did mutate

Intended
"Peirce" City, Missouri was named after Andrew Peirce, Jr. the president of the St. Louis-San Francisco Railway. After a Post Office screw up, the town became named Pierce City.

Original
Not sure about this clue.. my guess is Eisenhower, because 1. this follows the rule and, 2. his first name was originally "David Dwight", but he went by "Dwight David" - swapping the order like "i" and "e" in this rule. No (US) states have "ie" or "ei" or changed their original names, as far as I know.

And for the hint:

Some teachers find this rule problematic, because there are so many exceptions to it

• You have the answer, but none of the reasons (except the hint). Take another look at the tags. I'll hold off accepting this for a bit, to give someone a chance to explain the reasoning. – Neon612 Jun 14 '16 at 21:10

Wild guess:

John Tyler was an exception to the norm. He served as President of the United states longer than any other who was not elected. Starting with Andrew Jackson (son of jack) - then three more (Tyler is the third from Jackson)... perhaps the riddle suggests Tyler mutated from Vice President to President without a single vote being cast for him.

• I thought that John Tyler was the singer from Aerosmith. No? – Chowzen Jun 14 '16 at 0:22
• Good guess, but remember I'm looking for a saying or cliche. I don't want to give too much away just yet, though. – Neon612 Jun 14 '16 at 13:20
• @Chowzen that's Steven Tyler – Moose Jun 14 '16 at 19:14
• @Moose Yes, it was a joke. :) – Chowzen Jun 14 '16 at 20:10
• Tippecanoe and Tyler Too! – zipzit Jun 14 '16 at 21:38