The young Gers fell to a narrow defeat to the Bees who netted twice in the final 11 minutes after an evenly-fought contest.
Rangers lined up with an especially young side once again, which included starts for Josh Gentles and Calum Adamson, both still 16-years-old.
Speaking to RangersTV after the contest, McCallum said: “I think sometimes in football you don’t get the result that your performance deserves, and today was one of those days.
“The players felt that after the game, and it adds to the frustration that the goals were avoidable.
“We knew it was going to be a challenging game, but the overriding feeling is that we had some really top individual performances and that’s what we’ll focus on more than anything else.
“Calum was excellent, and there were a few people who came up to me after the game and made a similar sort of comment.
“He’s the first name that is spoken about, but it’s unfair to say he’s the only name because there are more: I thought Zander Hutton had a strong performance, Leyton Grant too, and a few older ones albeit there weren’t many included in the group.”
Indeed, there were plenty of positives for the Light Blues to take, with Brentford providing stiff opposition both with their shape in and out of possession.
Opportunity knocked for the Gers youngsters with several of the B Team regulars missing this afternoon, and McCallum believes they seized their opportunity.
He added: “Ultimately when you talk about developing young players, today was a good opportunity to see exactly that.
“We weren’t sure what the squad would look like, and I thought there may be one or two players needing minutes, but of course the first-team playing on Thursday night takes priority and that brings opportunity for the young ones who I thought were excellent.
“You look through the group and you also have Josh Gentles and Chris Eadie splitting time at the top end of the pitch; Archie Stevens and Paul Nsio are still Under-18s.
“You look through the team and there are a lot of players getting different challenges. At the moment it’s probably a group of individuals making up a team, but we’re trying to perform as a team and get individual benefits at the same time.
“We’ve got that in the last few games, but what we’ve not got is the feeling of a result because sometimes performances don’t match results.”