A couple of other points are probably worth mentioning. The first is obvious: no supplementation is going to compensate for years of poor dietary habits, so any study that uses any compound in an interventionary way will yield significant beneficial results. This is as true of omega-3 fatty acids as it is of vitamins or minerals.
The second is less obvious but potentially more useful. More than two decades ago, Bernard Gesch of Oxford University was asked to create a study to see if giving 1g of omega-3 fish oil supplements to long-term prisoners would reduce cardiovascular disease sufficiently to be worth the expense. His study yielded no statistically significant difference at the end of the 6-month trial between the control group and the experimental group (this was a properly designed double-blind placebo-controlled study). What he did discover, to everyone’s surprise, was that prisoners in the experimental group showed dramatic reduction in agitation during the period of supplementation; several voluntarily began self-study programs while others ceased being “problem offenders.” Gesch’s results have been replicated many times since (most notably by a Dutch team about 18 months later) and have been independently observed in all cases.
So anyone whose children are having trouble focusing, and anyone suffering from anxiety or chronic depression, could usefully consider supplementing with omega-3 at around 1.5g to 3g per day. While such supplementation won’t cure any underlying problem it may ameliorate symptoms to a noticeable degree.
Below is a link to a 2006 article in the UK Guardian newspaper that summarizes research up to that point in time: https://www.theguardian.com/politics/2006/oct/17/prisonsandprobation.ukcrime