Five years ago, the iPad was one of Apple's (NASDAQ:AAPL) biggest growth drivers. But for the past few years, iPad sales have declined steadily, offsetting growth elsewhere within the company.

Since March, Apple has thoroughly revamped its iPad lineup. Last week, at its Worldwide Developers Conference, Apple updated the 12.9" iPad Pro and introduced a brand-new 10.5" version of the iPad Pro. These new devices may help Apple stabilize its iPad sales -- but a return to growth will depend on the success of Apple's cheaper iPads.

The iPad lineup as of March 2017

Apple has replaced most of its iPad lineup this year. Image source: Apple.

iPad sales have been crashing

Demand for Apple's iPad peaked way back in fiscal 2013, when the company sold 71 million iPads. Since then, iPad sales have been in free fall despite numerous product updates, price cuts, and an aggressive move into the enterprise market. Apple sold fewer than 46 million iPads last year, and iPad sales continued to decline at a double-digit rate in the first half of fiscal 2017.

One big reason for the sales woes is that the iPad became "good enough" for most users years ago. As a result, customers are keeping their iPads for many years. Additionally, when upgrading their devices, many customers have opted for cheaper models rather than Apple's latest and greatest iPads. Indeed, more than 70% of total iPad usage still comes from devices that were introduced in 2013 or earlier, according to Fiksu.

The launch of Apple's "Plus" line of 5.5" iPhones has also contributed to the iPad's decline. The availability of large-screen iPhones has convinced some former iPad users that they only need one mobile device.

The iPad Mini lineup has been particularly hard hit by this shift in consumer preferences. As a result, Apple now sells only one iPad Mini version (the iPad Mini 4) with a single storage option (128 GB). Apple may discontinue the iPad Mini entirely in 2018, as my Foolish colleague Ashraf Eassa explained last month.

The new iPad Pros are here

The new iPad Pro models represent Apple's latest attempt to reenergize demand at the high end of the tablet market. The new A10X processor is 30% faster than the A9X from the previous iPad Pro models and delivers 40% better graphics performance. This has enabled it to double the screen refresh rate. As usual, the cameras and various other features have also been upgraded.

A person writes on an iPad Pro with an Apple pencil.

Apple has significantly upgraded the iPad Pro's performance. Image source: Apple.

Furthermore, for the 10.5" iPad Pro, Apple has shrunk the bezels relative to the previous 9.7" model. As a result, it offers 20% more screen real estate while being similar in size to the outgoing model. The 10.5" iPad Pro will still weigh just one pound.

Apple probably has relatively modest sales expectations for the 12.9" iPad Pro, which has been a niche model since its late-2015 introduction. With a starting price of $799, and a maximum price of $1,229 for a 512 GB Wi-Fi plus cellular version, the 12.9" iPad Pro is mainly targeted at corporate customers.

The 10.5" iPad Pro could be more appealing to iPad fans looking to upgrade older models. Yet with a starting price of $649, it's no bargain, either. Over the past year -- despite the launch of the first-generation iPad Pro models -- the average selling price for an iPad has hovered between $400 and $500. Clearly, there's a limited amount of interest in pricier models.

The basic iPad could be a bigger hit

Due to their high selling prices, the new iPad Pro models should generate plenty of revenue and profit for the company even if their absolute sales numbers are relatively modest. But in terms of driving a return to unit sales growth, the new basic 9.7" iPad released in March will be more important.

The new 9.7" iPad represents a very modest upgrade to the iPad Air 2. However, since tens of millions of iPad users are still using pre-iPad Air devices, the new iPad's modest specs shouldn't be a big barrier to sales.

The main attraction is its modest $329 starting price. This could encourage price-sensitive customers to try the iPad, while giving owners of older iPad models a cheap upgrade option.

With the new iPad Pros, Apple has once again delivered its best iPads yet. However, what customers really seem to want is a cheaper full-size iPad. They finally got that this year. We'll see in the next few quarters whether this is enough to get iPad sales growing again.

Adam Levine-Weinberg owns shares of Apple and is long January 2018 $90 calls on Apple, short January 2018 $140 calls on Apple, and short February 2018 $160 calls on Apple. The Motley Fool owns shares of and recommends Apple. The Motley Fool has a disclosure policy.