SANTA CLARA -- Colin Kaepernick was a high school quarterback when he first threw passes alongside Josh Johnson, doing so under the private tutelage of Bay Area quarterbacks guru Roger Theder.
Kaepernick and Johnson are learning technique together again, and Jim Harbaugh is coaching them up for what promises to be one of the 49ers' best training camp battles.
Alex Smith is the undisputed starter. Turlock's Kaepernick, a Pitman High graduate, and Johnson, an Oakland Tech graduate, are the leading candidates for the No. 2 slot.
Also competing is Scott Tolzien, who was the 49ers' third-string quarterback last season as a rookie.
"Josh is a great guy, and I'm good friends with him," said Kaepernick, a second-round pick last year out of Nevada. "At the same time, we know it's a competition when we step on the field."
For the first time since the offseason program ended in mid-June, all four quarterbacks are back on the field this week. Rookies and selected veterans also have taken part in practices Monday and today in advance of Friday's first full-squad practice at training camp.
Johnson is the newcomer of the group, having spent the past four seasons with the Tampa Bay Buccaneers.
But he played at the University of San Diego under Harbaugh and fit right in with the 49ers system during spring workouts.
Asked recently about the depth chart, Johnson said: "My mindset is to be in control of the offense and run the show. When you're under center, it's your offense. There's only one quarterback out there at a time."
For the record, Johnson, Kaepernick and Harbaugh have not returned to the racquetball court since Johnson's free-agent visit to the 49ers before he signed a two-year deal in March.
Kaepernick barely played his rookie season. He had a one-snap debut in Philadelphia and fourth-quarter cameos in home routs of Tampa Bay and St. Louis.
He was 3 of 5 for 35 yards, a small sample size to gauge his readiness. (In the preseason, he was 21 of 50 for 257 yards with no touchdowns and five interceptions.)
"I just want to keep working on getting my feet quicker, getting through reads quicker and taking pressure off the offensive line," Kaepernick said.
NFL quarterbacks not only have to work on reading defenses for pass plays but also for run calls, especially for a 49ers offense that thrived best behind a power run game last year.
"That's something we work on every day, so I'm very comfortable with it," Kaepernick said.
Asked about why some of his passes sailed high early in offseason practices, Kaepernick shrugged and said it depended on the day, pass and route.
Asked if he is better at passing on the run or when he's stationary, Kaepernick responded: "I'm very good at both. It just depends on what play is called and what I have to do."
On Monday, rookie running back LaMichael James said Kaepernick has helped bring him up to speed with the 49ers' massive playbook.
"He's just been at the house hanging out, and so we go over things here and there," Kaepernick said of James. "He's a great athlete and has a lot of tools that we can use. That's something we want to make sure we get ready for the season. ...
"We've got a little of that 'option-bond' from college (systems)."