Tongue Twisters are good for encouraging a student to speak at a slower rate and to be more precise in their speech sounds.  Here are some to try on for size.

I thought a thougt.  But the thought I thought wasn't the thought I thought I thought.  If the thought I thought I thought had been the thought I thought, I wouldn't have thought so much.

Once a fellow met a fellow in a field of beans.  Said a fellow to a fellow, "If a fellow asks a fellow, can a fellow tell a fellow what a fellow means?"

A skunk sat on a stump.  The stump thought the skunk stunk.  The skunk thought the stump stunk.  What stunk the skunk or the stump?

How many cans can a canner can, if a canner can can cans?  A canner can can as many cans as a canner can, if a canner can can cans.

A tree toad loved a she-toad

Who lived up in a tree.

He was a two-toed tree toad

But a three-toed toad was she.

The two-toed tree toad tried to win

The three-toed she-toad's heart,

For the two-toed tree toad loved the ground

That the three-toed tree toad trod.

But the two-toed tree toad tried in vain.

He couldn't please her whim.

From her tree toad bower

With her three-toed power

The she-toad vetoed him.

Black bugs blood, Black bugs blood.  Black bugs blood.

Rubber baby buggy bumpers.  Rubber baby buggy bumpers.