The band's name seems to be spelt usually as In-Betweens with a hyphen, or as In Betweens, but on their singles it appears as one word, Inbetweens. See label shots at 45Cat.com.
Single on Impact by Dunedin band formed 1967 when its members were still at high school. They were managed by the mother of founding members Tony and Paul Rabbett. Rob Guest (1950-2008), better known now for his stage performances in Phantom of the Opera and Les Miserables, joined The In-Betweens in 1970 as vocalist. They became a top South Island band after successes in national band competitions and removed to Sydney in 1972 before breaking up.
Boom Sha La La Lo was one of two charting singles by The Inbetweens: the other was Make A Wish Amanda (1971, #20 NZ).
Single on Fable from the album Natural High, by highly regarded and much-loved Melbourne singer-songwriter and multi-instrumentalist Hans Poulsen (b.1945) formerly with Eighteenth Century Quartet, the band he'd formed as 18CQ. Operating somewhere in the folk-pop-country-hippy-baroque neighbourhood, Poulsen worked in Australia, Britain and the US over several decades, writing hundreds of songs for himself and for other artists in Australia and beyond.
Boom-Sha-La-La-Lo was co-written by Bruce Woodley of The Seekers and arranged by John Farrar from The Strangers. Monty And Me by The Zoot (1969, #16 Melbourne, #12 Brisbane), is another Woodley-Poulsen composition.
Other Hans Poulsen singles that charted in Australia:
• Rocking Chair (1968, #23 Perth)
• Comin' Home Late Again (1969, #31 Melbourne, #34 Brisbane)
• Light Across The Valley (1970, #3 Brisbane, #2 Adelaide)
• Stick Of Incense (1971, #26 Adelaide).
Poulsen's compositions recorded by other artists include:
• Jamie: Johnny Farnham (1968, #30 Sydney #7 Melbourne #1 Brisbane #1 Adelaide)
• Rose Coloured Glasses: Johnny Farnham (1968, #10 Melbourne, #7 Brisbane, #7 Adelaide)
• Everybody's Girl: Larry's Rebels (1968, #6 NZ)
• Lady Scorpio: The Strangers (1969, #5 Melbourne) and Fourmyula (1969, #7 NZ).
References, further reading: 1. Eighteenth Century Quartet history by band member Ted Baarda (2001), including Hans Poulsen bio [Internet Archive page]. 2. Eighteenth Century Quartet (18CQ), history at Milesago. 3. "Hans Poulsen" by Ian McFarlane, The Encyclopedia of Rock and Pop (1999), pp 491-492.