In a very recent study done in Switzerland this year and published on June 12 this month, it was shown that kids betweent he ages of 7 and 10 reached a higher level of writing performance both in the quality and the quantity.
This was the result of a study done with 44 classes in Switzerland over the course of three years.
The first group used an internet platform to write, with the result that their texts were more directed to the reader, livelier in the use of language and better in terms of spelling (in German- the normal school language) even thought the texts were not corrected by the teachers.
A further remarkable difference is that the quality of writing between boys and girls was about the same in this group, where in the paper and pen group the mainly the girls profited from the writing tasks.
If you understand German, you can find the results here.
I find that these results confirm my ideas about the use of blogs and other on-line platforms for as early as primary school lessons.