Sorry for the delay in replying to this, I kept meaning to! A rough breakdown of what our group did:
1) We found the source for the claim which was at the SNP manifesto launch. Within the transcript was a figure of 9.4%, which was key to determining the particular productivity statistics that were being referred to.
2) We looked at the labour productivity statistical releases by Scottish Government, and within the publication archive the February release showed that "output per hour" increased by 9.4% between 2007 and 2015. Therefore "output per hour" is the definition of productivity the claim referred to.
3) We looked at the labour productivity statistical releases by ONS to compare to UK figures, and over the same time period "output per hour" has remained static.
So our conclusion was "mostly true" (although it's been so long now I can't remember all the details!).
Afterwards I had a look at some other data sets and there was an interesting ONS one which compares all the UK regions. Only London and the South East are above the UK average, and Scotland is 4th behind the East of England (although it looks as though it is about to overtake it into 3rd place).
Also it's really important to note that the Scotland (and other regions') figures are "only in relation to the UK average". It doesn't mean that Scotland's productivity actually increased by that amount. Indeed, it could have decreased! You would need to look at the raw data before indexing to determine the actual trend.
Anyway, I found it a really interesting workshop and it was great to see everyone's approaches to this.