An interim report on the King's academy has concluded it is "an inclusive, harmonious and orderly community" making satisfactory progress.
The report follows last week's decision by inspectors to place the Unity academy in special measures for its unacceptable education standards and poor morale.
Steve Sinnott, general secretary of the National Union of Teachers, said Unity's damning report was a warning to ministers that the academies programme was "going nowhere".
The differences between the academies' reports are striking because the two appear very similar on the surface.
Both are in futuristic buildings on the south east of Middlesbrough and cater for around 1,100 pupils. Each has faced challenges uniting pupils from the pairs of schools they replaced and both have been criticised for expelling too many students.
King's attracted controversy when it opened in 2003 because it is sponsored by the Emmanuel Schools Foundation, which has encouraged the teaching of creationism. The foundation was established by Sir Peter Vardy, the multi-millionaire car-dealer.
Unity's sponsor, support services company Amey, appeared better placed to back an academy. It has been involved in schools projects including the outsourcing of education services in the London borough of Waltham Forest.
But inspectors said Unity's leadership was fragile and unsatisfactory, and they were deeply concerned by its projected budget deficit of more than pound;1 million.
In contrast, they said King's was very well-led, with inspirational direction from Nigel McQuoid, its principal.
Teacher turnover and retention was described as a severe problem at Unity, where staff morale was low and as many as a third of teachers were absent each day.
At King's, pupil and teacher morale was generally positive and no significant staffing problems were found.
Even the academies' new buildings were of differing quality. Inspectors said those at King's were well-designed and attractive while Unity's were "impressive and futuristic, but not entirely fit for purpose, lacking a playground, relaxation areas for staff and sufficient space for the pupils to eat in comfort".
The Vardy academy's report was not entirely glowing. King's was criticised for its weak day-to-day planning and narrow range of teaching methods, which left pupils bored in some lessons.
However, the academy had half as many unsatisfactory lessons as Unity and twice as many students with five A* to C grades at GCSE.
One possible reason for the difference is the number of pupils on free school meals: half of the students at Unity are eligible for them compared to a third at King's. Another is that pupils at Unity had to study in their old schools' buildings for two years before moving to the academy's new site last September.
Joe McCarthy, chair of the Unity Trust board and Mark Lang, recently-appointed principal, said in a joint statement: "No-one should underestimate the scale of the task which has faced Unity since its inception - taking over from two struggling schools, dealing with underachievement and low expectation, and having to operate in old and decaying buildings for the first two years, only moving to the academy site nine months ago."
Unity will form a federation with the nearby Macmillan city technology college from September, when the two schools will be managed by a joint board of governors and a federation director.
King's and the other two Vardy-sponsored schools, Emmanuel college in Gateshead, and the soon-to-open Trinity academy near Doncaster, are also moving towards a federation approach. Mr McQuoid is to be promoted in September to overall schools director for the Emmanuel Foundation and will oversee all three schools.