Your description calls to mind an article on the
Davidson Database, titled
Gifted children: Youth mental health update.
This article was also mentioned in a post here in October 2014, which may be where you previously saw it?There is a section about midway through the article subtitled
Special Needs of Gifted Children, which describes these four needs in detail:
A. Need for a challenging education.
B. Need for "true peers."
C. The need for responsive parenting.
D. The need for adult empathy.
In the clinical experience of the author, a range of behavioral problems (from daydreaming to school refusal) have resulted when the school curriculum was not sufficiently challenging.
The next section of the article, subtitled
Giftedness and Self-esteem, highlights findings of a study by Miraca Gross:
In her study of exceptionally gifted children, Gross has reported that the self-esteem of exceptionally gifted students tends to be significantly lower than the self-esteem of average students, especially when the school is unwilling or unable to allow them access to other children who share their levels of intellectual, oral and psychosocial development. Thus the gifted child is placed in the forced dilemma of choosing to minimize intellectual interests and passions for the sake of sustaining peer relations or of pursuing intellectual interests at the cost of becoming socially isolated in the classroom. As Gross poignantly added "The gifted must be one of the few remaining groups in our society who are compelled, by the constraints of the educative and social system within which they operate, to choose which of two basic psychological needs should be fulfilled."
The thread on Buzzwords includes a list of resources providing more information on the positive benefits of flexible cluster grouping by readiness and ability.
Here's a post including reasons which some schools have given for not cluster-grouping children by similar level of ability and readiness. 
These are examples of working against the development of positive self-esteem and mental health in gifted pupils.These
observations may signal that a change is needed and may be overdue.
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NOTE: The article "Gifted children: Youth mental health update" by Julia Osborn, 1996, published by Division of Child and Adolescent Psychiatry, Schneider Children's Hospital, is backed up on WayBack Machine, Internet archive.
Links:
1) article -
https://web.archive.org/web/20200112034938/http://www.davidsongifted.org/search-database/entry/a10170
2) list of archive dates/times -
https://web.archive.org/web/*/http://www.davidsongifted.org/search-database/entry/a10170
