Making up plans on the hoof is how Jack tends to work. Think of something and go for it, and if it doesn't work out, improvise some more!
"Please, high school kids are a little young for me!" he protests, and then grins at Ianto. "I'm sure you'll think of something," he assures him, voice rich with promise.
"And of course we're coming with you," he says, turning back to Spike, sobering abruptly. He gives Spike a serious look. "The least we can do is be there for you, help you through it."