MANSFIELD, Mass. — So, are Jonas Brothers for real?

Well, 90 minutes might have been a bit long for the teenage rock trio at the Comcast Center last night, with a few too many ’80s-rock retreads in the set and a few uninspired ballads thrown in for the teen-girl set who seemingly screamed from the minute the doors opened yesterday afternoon. But between the length of the show, the 12-piece string section and the heavy concentration of new songs, they seemed to be making a bid for respect, and last night it wasn’t a bad one.

With lead vocals split between Joe and Nick Jonas (with Nick dividing his time between drums and guitar) and Kevin Jonas playing guitar, they’ve certainly got the teen-idol basics down: good looks, and singing and stage moves that are organized yet shaggily exuberant enough to convey a sense of fun. Not much in the way of stage banter, but the sight of Joe Jonas emoting “Still In Love With You” half-covered in foam from the huge hoses of stuff they shot at the audience was a humorous moment.

While some of their older songs featured writing help from the guys in Fountains of Wayne, their own stuff is showing promise. And judging from the songs they did from it last night, their new album, A Little Bit Longer, which comes out Tuesday, isn’t much of a departure, but neither is it a letdown.

While the lead single, “Burning Up,” was a fairly generic slice of teenpop, “BB Good” was a strong bid at a high-school version of Cheap Trick; “Lovebug” was strongest in its mostly acoustic intro, with a nice reggae-like bounce; “Tonight” was a dance-floor rocker with an aerobic tempo and a nice falsetto hook, and “A Little Bit Longer” was a nice ballad (coming after videotaped and spoken testimony from Nick Jonas about his life with diabetes) that showed good grasp of the basics of Beatle-esque songwriting, though it didn’t need the power-ballad treatment it got at several points.

They also made a nod to their appearance in the Disney movie Camp Rock, with a mostly acoustic “Gotta Find You” and a guest appearance by co-star (and opening act) Demi Lovato for “This Is Me.” “I’m Gonna Getcha Good” was a Shania Twain cover that lagged, but hits such as the breakneck “Goodnight and Goodbye” and “Hold On” (with a glorious passing chord in the chorus — a little detail that speaks volumes about their pop sensibility) kept things moving early on.

Their opening song last night, “That’s Just the Way We Roll,” is a carbonated, high-sugar shaken-up soda of a song, includes a joke about losing a dance battle against Hanson. It’s not a bad comparison. While it would be surprising to see Jonas Brothers filling the Comcast Center 20 years from now, it would be far less so to find them making respectably received records and playing somewhere. They might have to make a conscious decision to drop the appeals to the teen set before the teen set drops them, though.

Lovato opened with a fairly generic smattering of Disney Channel power pop and power ballads, sung with a run-of-the-mill voice and, too often, an actorly emoting.

rmassimo@projo.com