A School Like Mine

Scoil mar an scoil s'agamsa
Scoil mar mo scoilsa
Scoil cosúil le mo cheannsa (though apparently you can't use this expression if you name the subject - is that right ?)

all are correct (in standard Irish the 2nd one would be "mo scoilse").
The last one is correct too.
It depends on the context...
But without context, if I had to translate the sentence, I'd probably say the last one.

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Is fearr Gaeilg na Gaeltaċta ná Gaeilg ar biṫ eile
Agus is í Gaeilg Ġaoṫ Doḃair is binne

It's the name of a book - this is the original title, but as usual the translation isn't the same. I find it very annoying when you put the two (or three) versions side by side in front of the children and they don't resemble the original - when even the title is different it often means that the translation gets even worse as you go through the book.
In Irish it's published as - Seo í mo scoil - and in French as - Ma super école (and Gallimard Jeunesse obviously assumed that they knew better than Dorling Kindersley and thought it necessary to completely change the front cover, - it didn't sell, so now it's out of print).

Here's the second part of the title - A Unique Celebration of Schools Around the World.

Does this work ?

Ceiliúradh Uathúil na Scoileanna Timpeall an Domhain/Ar Fud an Domhain

"uathúil" ? i'm not familiar with this word... I'm not sure it's meant to mean what you are trying to say here...
What does "unique" mean here?

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Is fearr Gaeilg na Gaeltaċta ná Gaeilg ar biṫ eile
Agus is í Gaeilg Ġaoṫ Doḃair is binne

It's in the Teanglann dictionary, there's also - sainiúil - and - ar leith. The 'translation' that's on the cover of the Irish edition is - 'Scoileanna ar fud an domhain trí shúile páistí'.

I'd say 'uathúil' = 'unique' in its core sense of 'the only one of its kind', but in its looser sense of 'special, remarkable' etc., then 'ar leith' would be more appropriate.

So - Ceiliúradh ar leith na Scoileanna Timpeall an Domhain - how's that?

putting "ar leith" between a noun and its genitive extension sounds weird.
Maybe: Ceiliúradh ar leith do na scoileanna timpeall an domhain
With a preposition (I'm not sure "do" is the right one, but with "ar" it means something else...) it looks better.

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Is fearr Gaeilg na Gaeltaċta ná Gaeilg ar biṫ eile
Agus is í Gaeilg Ġaoṫ Doḃair is binne

D'accord. En fait je pensais le mettre après - na Scoileanna - mais dans ce cas-là, on comprendrait que c'était les écoles qui étaient uniques et pas ceiliúradh.

There's another series of Dorling Kindersley books that have been published in Irish - Tá mé ag fás. Again that's not the same as the original title - See How They Grow - in French for the books it's Regarde-les Grandir and for the DVDs, it's Regarde-moi Grandir. It would a nice idea if they could bring out the DVDs in Irish.