According to the article "A theory of team coaching" team coaching can foster team effectiveness except when

		the group performance processes that are key to performance effectiveness are relatively unconstrained by task or organizatonal requirements
		coaching behaviors focus on member's interpersonal relationships
		coaching interventions are made at times when the team is ready for them and able to deal with them.
		the team is well designed and the organizational context within which it operates supports rather than impedes team work.