Each Friday from now until the end of May, Jason A. Churchill, who covers the MLB draft for ESPN Insider, will look at the high school prospects whose stock is up and whose stock is down heading into the draft, which begins on June 4.

A number of top prep prospects are finishing up their seasons. So at this point, their stock is only changing due either to growing signability concerns or the improved stock of those still playing. It’s fluid, but it can only take one team’s assessment of a player to change his draft stock.

Here’s an overall look at which prospects have helped and hurt their draft prospects since last week.

STOCK UP

Mitch Brown, RHP, Century (Rochester, Minn.)

Brown's stock is up significantly from a year ago thanks to improved velocity, command and a more consistent delivery that promotes better arm action and deception. The 6-foot-2, 215-pound San Diego commit has been up to 95 mph, and his high-80s cutter is an added weapon. He began the season as a likely Day 2 pick -- perhaps somewhere between rounds four and six -- but has pitched his way into the sandwich-round conversation and may not get past the hometown Twins at No. 42.

Alec Rash, RHP, ADM (Adel, Iowa)

Rash flashed low-to-mid 90s heat in bullpen sessions for scouts as he prepared to start his season (Iowa high school baseball starts in May) and is rising up the charts as a result. Scouts saw 90-92 last summer, but he has added velocity between seasons. He's committed to the University of Missouri, but he could land as high as the compensation round. He gets good plane on his heater and his breaking ball has flashed as an above-average pitch. It would be a surprise if he lasted beyond the second round.

Ty Hensley, RHP, Santa Fe (Edmond, Okla.)

Hensley has the physical tools of a first-round power arm, and that's exactly where ESPN Insider's Keith Law has him going in his latest mock draft. Hensley could potentially go as high as No. 9 to the Miami Marlins, a club that loves to take high school power arms and ride out the upside. The 6-foot-5, 220-pound Hensley is committed to Ole Miss, but there's a good chance he doesn’t step foot on campus.

D.J. Davis, Stone County (Wiggins, Miss.)

Davis' signability helps his case -- he's not signed to a Division I school and will attend Meridian Community College and re-enter the draft next June should he not sign this summer. But his 80-grade speed, plus defense in center and improved showing at the plate not only has sent his stock soaring but it may get Davis into the first round. He's a left-handed stick who has displayed selectivity and added pop in 2012 and appears destined to be off the board in the top 30 picks.

Others Trending Up

Giovanni Brusa, OF, St. Mary’s (Stockton, Calf.)

Lance McCullers Jr., RHP, Jesuit (Tampa, Fla.)

STOCK DOWN

Zach Eflin, RHP, Hagerty (Oviedo, Fla.)

Eflin may see his stock drop slightly due to a late injury. Eflin missed about a month with a strained triceps and returned last week to mixed reviews. There's a chance the 6-foot-5, 200-pound right-hander, with his 91-95 mph fastball and polished feel for pitching, could again rise into the top 15 if the triceps issue proves to be a one-time problem.

Hunter Virant, LHP, Camarillo (Calif.)

Virant could be the victim of so many other prospects gaining steam, including a number of prep and college arms. He's not the most projectable of arms, but he could add strength to his 6-foot-2, 175-pound frame that could help him add velocity and improve his ceiling from No. 3 starter to potential No. 2 or better. Former first-round pick Tyler Skaggs, now a top prospect in the Arizona Diamondbacks organization, brought a similar profile to the 2009 draft.

Matt Olson, 1B, Parkview (Lilburn, Ga.)

Olson has big-time raw power and performed well this spring, but is limited to first base and there are other bat-first or bat-only prospects at the prep level that carry higher grades, including Mitch Nay of Hamilton (Chandler, Ariz.) and Joey Gallo of Bishop Gorman (Las Vegas). Olson has a simple swing, but he doesn't incorporate his lower half much and employs a near dead-hand start, which could limit his power against good pitching.

Jason A. Churchill covers scouting, player development and the MLB draft for ESPN Insider, as well as Prospect Insider, where he's the founder and executive editor. You can follow him on Twitter @ProspectInsider and email him at churchill@prospectinsider.com.