With a stock market still hitting new, record highs, stocks that double in value in a year's time may not seem like much of an achievement. Yet the S&P 500 is up only 15% this year and the Dow is 20% higher, so a stock that has run up 100% or more is still pretty significant.

Of course, investors shouldn't go out looking to make that kind of return in so short of a time but instead, view it as a happy circumstance when it does occur. So let's find out why Conn's (NASDAQ:CONN), National Beverage (NASDAQ:FIZZ), and iRobot (NASDAQ:IRBT) were all able to double in value or more in the past 12 months.

Conn's storefront

Image source: Conn's.

Conn's (up 202%)

The best performer of the three, specialty retailer Conn's, has tripled in value this past year. Helped in good measure by results like this past quarter, where it reported a surprise profit. Wall Street had been looking for a loss of $0.02 per share, but Conn's was instead able to notch a $0.26-per-share adjusted profit.

As a part of a turnaround effort, the retailer that specializes in furniture, mattresses, consumer electronics, and home appliances has been cutting costs and tightening up its credit portfolio, which allowed it to benefit from its improved performance and exceed its own expectations. It was able to tighten underwriting standards and generate higher yields in its credit business while same-store sales are expected to improve.

The rally in its shares might end briefly, however, since the devastation of Hurricane Harvey is expected to hurt sales next quarter. During the storm, Conn's was forced to close 23 stores, its distribution and service centers in Beaumont and Houston, and its Beaumont corporate office. Reacting to such a development would be the sort of short-term thinking investors should avoid. Rather, they ought to focus on the long-term turnaround plan Conn's has been successfully implementing.

Cans of Lacroix water

Image source: Lacroix Water.

National Beverage (up 168%)

With soda consumption falling, the smart bet has been on water, but not just the kind you can pull out of your kitchen faucet. Rather, the real gains are being made in sparkling water, and National Beverage's bet that LaCroix will become the leading sparkling-water brand is paying off well.

National Beverage has long provided consumers with a line of sugary beverages under its Shasta brand, but it wasn't until it acquired LaCroix that its business really took off. Similar to how SodaStream International switched its focus from make-it-yourself at home soda to DIY seltzer, which led to a rebound in its business and an astronomical rise in its own stock, National Beverage has quickly been able to take on the biggest brands in the sparkling-water industry, including stalwart Perrier.

The beverage maker just reported fiscal 2017 first-quarter earnings that saw it notch its 11th consecutive quarter of revenue and earnings growth. As Chairman and CEO Nick Caporella stated in the earnings release, "While financial performance is ultimately the healthy condition of management's purpose ... it starts with a naturally essenced strategic growth plan, and, certainly, this first quarter is more than robust."

While such flowery language is a hallmark of National Beverage releases, when your results have been as effervescent as the sparkling water maker's, you can be forgiven for providing such frothy verbiage.

iRobot Roomba vacuum

Image source: iRobot.

iRobot (up 140%)

Leading consumer robot maker iRobot is best known for its Roomba robotic vacuum cleaner, but it also makes devices that will help mop your floor, clean your gutter, and clean your pool.

While iRobot's ascendance has been more than just any one event, the recently held Amazon.com (NASDAQ:AMZN) Prime Day sales event is an indication of the kind of marketing power the robot maker still holds. iRobot's Roomba 652 Robotic Vacuum Cleaner was one of the top 10 selling items that day, and as the company declared in a press release celebrating the achievement: "We sold more than twice the volume sold on Prime Day in 2016, which was twice what the volume sold in 2015. The Roomba 652 was ranked No. 1 in robotic vacuum cleaners, No. 1 in all floor care, and No. 2 in all home and kitchen for 2017 Prime Day."

That kind of performance is going to reflect well in the upcoming earnings report, but last quarter it was reporting revenue had jumped 45% year over year, and that was without any big promotional event. They beat guidance on both top and bottom line for the year, and the stock has jumped to an all-time high.

Investors who have stuck with iRobot have cleaned up by owning its shares.

Rich Duprey has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Amazon and iRobot. The Motley Fool owns shares of SodaStream. The Motley Fool has a disclosure policy.