I think that most investors would agree that volatility was the prominent theme of the March quarter this year.

As the graph below shows, the S&P/ASX 200 (Index: ^AXJO) (ASX:XJO) lacked any real direction over the period but at the same time, market moves were aggressive when they occurred. This was the case in both directions, with gains and losses of more than 1% seemingly routine during the quarter.

Source: Google Finance

Source: Google Finance

Overall, the broader market has declined by around 4% since the start of the year with the big banks being the biggest detractors from the market’s overall performance.

Unsurprisingly, those investors who “picked” stocks rather than owned portfolios that mirrored the index would have a far better chance of delivering positive returns over the quarter.

With that in mind, here are seven stocks that have delivered impressive returns since the start of the year:

Medical Developments International Ltd (ASX: MVP)Up 43%

Medical Developments is the company behind Penthrox (more commonly known as the green whistle) which is used for pain relief in emergency situations. The company’s market capitalisation is now approaching $300 million despite it generating revenues of less than $6 million in the first half of FY16. Investors clearly like the story and will hope the company lifts sales and profits in the not-too-distant future to justify its current valuation.

Medibank Private Ltd (ASX: MPL)Up 35.4%

The performance of Medibank Private shares has been surprisingly strong in 2016 as a result of an earnings upgrade and a better-than-expected first half earnings result. Medibank’s re-rating comes in the face of slowing policyholder growth and management’s forecast for lower profits in the second half as a result of increased marketing spend and higher hospital utilisations rates.

Fortescue Metals Group Limited (ASX: FMG)Up 36.4%

The fortunes of Fortescue are tightly linked to the iron ore price and the recent bounce in the commodity has helped relieve some pressure off the miner. The company still remains leveraged with a huge pile of debt on its balance sheet but it is working to reduce this in an efficient manner – something the market is pleased with.

South32 Ltd (ASX: S32)Up 37.1%

South32 is another miner that has seen a huge bounce in its share price this year thanks to a rebound in commodity prices. The company plans to further cut costs and capital expenditure in a bid to maintain cash and the market has also seen this as a positive.

Northern Star Resources Ltd (ASX: NST)Up 23%

Northern Star has been one of the best-performing gold stocks on the ASX as a result of its low cost production operations and its ability to consistently to pay out dividends to shareholders. There could be further gains to be made in the gold sector if global economic growth hits a significant hurdle.

Reject Shop Ltd (ASX: TRS)Up 28.4%

Shares of the Reject Shop have enjoyed a strong resurgence over the past 12 months as the company delivered on its turnaround strategy. Same store sales growth, reduced costs and an improved product mix have combined to deliver a remarkable improvement in earnings.

Idp Education Pty Ltd (ASX: IEL)Up 35.1%

IDP Education was spun-off from SEEK Limited (ASX: SEK) late last year and has lived up to some lofty expectations. The company provides international student placement services and specialised English language testing services in over 50 countries. IDP Education’s maiden profit result was robust with revenue and earnings growth of 24.6% and 23.2%, respectively.

Foolish takeaway

Very few, if any, of these companies strike me as being particularly cheap at the moment, but I would be inclined to keep a close eye on IDP Education and Northern Star as possible growth opportunities moving forward.

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Motley Fool contributor Christopher Georges has no position in any stocks mentioned. The Motley Fool Australia has no position in any of the stocks mentioned. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy. This article contains general investment advice only (under AFSL 400691). Authorised by Bruce Jackson.