Religious education teachers often sidestep controversial areas, turning what researchers believe should be a uniquely-rewarding subject into something bland and superficial.
A landmark event in Glasgow this week depicted an over-burdened subject served badly by tentative approaches.
Does Religious Education Work? launched research findings under the same name, billed as the most thorough exploration of RE in UK schools ever undertaken.
The three-year project sent ethnographers into 24 UK schools for 10 days in each, including seven in Scotland, to observe teaching of pupils' last year of compulsory RE; researchers believe their findings are applicable throughout the UK.
Teachers were often fearful of imposing their beliefs. Glasgow University's David Lundie found RE - more commonly known in Scotland as religious and moral education or religious, moral and philosophical studies - reduced to the "accumulation and naming" of "stuff".
Pupils covering Judaism might be asked to devise a menu for Hanukkah. Another lesson introduced 23 terms relating to Buddhism; on average, the teacher took less than three sentences to explain each one.
Such teaching "doesn't look at what it is to lead a life of faith", said Mr Lundie; it was reducing religions to "this bland other". Glasgow University colleague James Conroy said religions were made to look "eccentric and groundless".
Socratic techniques were employed as a "stalling tactic", said Glasgow University's Kevin Lowden, and some teachers perpetually asked, "What do you think?"
Researchers, also from King's College London and Belfast's Queen's University, found some teachers did not want to disclose their beliefs. One student teacher admitted being "scared of getting pulled up for it".
Glasgow University anthropologist Nicole Bourque said: "If you're expecting people to come forward with their views, I don't see any problem expressing your views."
Some teachers aimed for a neutral approach, which delegates widely dismissed as impossible. "There is no view from nowhere," Professor Conroy said.
There were several factors behind tentative approaches: non-specialist teachers; exam-driven pressure; and lack of support from management.
RE was a "dumping ground for other stuff" such as sex education, said Dr Bourque.
Treatment of sex within religions was usually misleading, said the report; by occasionally inviting pupils to discuss their own habits, RE was sometimes "at the cusp of legality."
Read `TESS' news focus next week for a four-page analysis of why schools need RE
ROW OVER TEXTBOOK STANDARDS
James Conroy revived a row about the standard of RE textbooks. At a conference last year, he criticised them for containing "no narrative, no critique, only lists of things to learn". That prompted angry responses in Scotland, with publishers and writers underlining that their books went well beyond course requirements.
This week, Professor Conroy stated: "The purpose of virtually every textbook we looked at was to achieve a pass at GCSE or Standard grade. They were self-consciously and unashamedly articulated in that way." He condemned a "disgraceful collusion between exam boards and writers of textbooks".