Lin, I am a bit of a duffer on concertinas, other than knowing they're either push-pull or chromatic.

Scottish accordion style is different from Irish principally because the Scottish ceilidh tradition (for the last century or so) is based on piano accordion, and the equally ancient Irish equivalent favouring the melodeon (if a free reed instrument is used). If you examine the difference in the dance styles of both traditions, you can start to perceive the difference in the music required. The fundamental difference is the use of the arms above the head and resting on the waist in the Scottish tradition, and the straight-by-the-side Irish equivalent. Both are wonderful art forms, so I hold no prejudice.

A musical difference would be that jigs are easier to play on the accordion than the melodeon. Also, the Scottish tend to use two piano accordions in a band, known as first and second box, which gives a massive sound.

You can hear the difference between the two traditions in the famous tunes. Tunes like Athole Highlanders, Dashing White Sargeant and Cock of the North capture the Scottish 'sound', whilst Father O'Flynn, Tobin's Favourite and the Kilfenora characterise the Irish sound, to my ear, at least. A musical difference is that the Scottish tunes tend to stay in major keys, whilst the Irish favour major/minor, or plain minor keys.

This is a ham fisted attempt at explaining my own take on this, and far finer musical minds can give you chapter and verse here. I can't even read music, so I really am ill equipped to postulate, but you did ask!